Since the birth of the Internet technology, the networks generally distribute data in the “best effort” mode without a guarantee of Quality of Service (QoS).
In the early 1990's, the Internet Engineering Task Force (IETF) proposed a model of Integrated Services (IntServ) to meet the requirement of the real time services such as Voice over IP (VoIP). Such a model for communication services is a stream-based mechanism with a guarantee of QoS, has a strict control over network resources and provides the guarantee of QoS for the application layer. However, this model suffers from the problem of extensibility, since each of the routers, through which a service stream passes, has to maintain a soft status for the model. Therefore, the IntServ model fails to be widely used.
The IETF further proposed a model of Differentiated Services (DiffServ) in 1998. The DiffServ model is a class-based mechanism with a guarantee of QoS, and is successful in the network deployment. However, this model provides only a relative guarantee of QoS, and fails to provide guarantee of QoS, especially in the case of an insufficient bandwidth.
The IETF further proposed a model of DS-Aware MPLS TE in 2002. The model incorporates the advantages of both the DiffServ model and the model of Multiprotocol Label Switching Traffic Engineering (MPLS-TE), optimizes the transmission resources and further improves the performance and the efficiency of the networks. However, this model suffers from a problem of square-of-N and has a difficulty in the inter-domain communication.
Based upon the prior art, neither a large bandwidth nor the DiffServ model can solve the problem of end-to-end QoS in reality. In recent years, the Dynamic QoS (DQoS), i.e. the dynamic session-based QoS-control mechanism, has gradually become a main research direction. This mechanism enables a Connection Admission Control (CAC) based on each session, a resource reservation and a dynamic policy distribution in the control plane, and implements the functions of service aware and strategy execution in the data plane. Such a mechanism can provide both a strict guarantee of QoS and a good extensibility. As a result, many standard organizations are addressing themselves to the similar mechanisms, in which the study of the organization of TISPAN (Telecommunications and Internet Converged Services and Protocols for Advanced Networking) wins the recognition of the industry.
Refer to FIG. 1, which is a schematic diagram of the basic network framework of the NGN established by the TISPAN, in which the NGN framework mainly includes a Service Layer 110 and an Internet Protocol-based (IP-based) Transport Layer 120.
Particularly, the service layer includes a Core IP Multimedia Subsystem 111, a PSTN/ISDN Emulation Subsystem (PES) 112, other Subsystems 113 (such as a streaming media subsystem, a content broadcast subsystem or the like) and an Application 114. In addition, some common components, such as a billing function, a user data management, a security management, a route database and the like, are also included.
The transport layer 120 is adapted to provide an IP interconnection for a User Equipment (UE) 130 with the introduction of two control subsystems, that is, a Network Attachment Subsystem (NASS) 121 and a Resource and Admission Control Subsystem (RACS) (122), both of which are adapted to hide the transport technologies below the IP layers of the access network and the core network.
Here, the Core IMS Subsystem 111 of the service layer mainly includes a Call Session Control Function entity (CSCF) which further includes a Proxy Call Session Control Function entity (P-CSCF), a Serving Call Session Control Function entity (S-CSCF) and an Interrogating Call Session Control Function entity (I-CSCF). Wherein the P-CSCF is the first contact point of the user equipment 130 within the Core IMS Subsystem; the S-CSCF is responsible for processing the network session status; and the I-CSCF is a contact point within an operator network for all subscribers with an access to the operator network or roamer within the service region of the operator network.
Now refer to FIG. 2 as well, which is a schematic diagram of the basic architecture of a RACS under the NGN R1 network architecture which is being established by the TISPAN, wherein both the QoS of the bearer network and the Network Address and Port Translator (NA(P)T) shall access the RACS and be controlled by the RACS.
The RACS mainly includes an Application Function entity (AF) 1, a Service-based Policy Decision Function entity (SPDF) 2, and a Core Border Gateway Function entity (C-BGF) 3, an Access-Resource and Admission Control Function entity (A-RACF) 4 and a Resource Control Enforcement Function entity (RCEF) 5. The relationship and interfaces between the RACS and related functions may refer to FIG. 2, wherein the control function of the NA(P)T may be achieved mainly through a signaling interaction between the AF 1, the SPDF 2 and the C-BGF 3. Other entities, such as the A-RACF 4 and the RCEF 5, may be applied mainly for the control over the QoS resources of the access layer.
The RACS provides an admission control function and a gateway control function (including a NA(P)T control and a DSCP flag). Here, the admission control function includes a check of subscription data saved at the network attachment subsystem based upon the specific policy rules and resources of the operator, an authorization, a check of the resource availability, and a verification of the consistency of a requested bandwidth with a predefined bandwidth and a user-used bandwidth and the like.
At present, in the above described NGN architecture established by the TISPAN, a Fixed Origination (FO) flow for an IMS session establishment is shown in FIG. 3. Here, the Fixed Origination flow for an IMS session establishment mainly applies to a user within its home network, and the UE of the user is located in the home network, but has an access to the IMS core network through xDSL (Digital Subscriber Line). The detailed implementation process is as following:
301: An originating UE sends a Session Initiation Protocol (SIP) Invite request, which contains a Session Description Protocol (SDP) Offer, to the P-CSCF, wherein the SDP offer contained in the SIP Invite request sent from the originating UE may be indicative of one or more media of a multimedia session;
302˜306: The SPDF reserves an IMS connection for the C-BGF, and may optionally request the C-BGF to perform a NA(P)T binding process;
307: The P-CSCF forwards the SIP Invite request, which carries the SDP offer and is sent from the originating UE, to a corresponding S-CSCF according to a next-hop CSCF of the originating UE recorded in the registration flow;
308: The S-CSCF determines a Service Profile upon receipt of the SIP Invite request with the SDP offer, and also invokes any initiation service logic required by the originating UE, including the procedure of performing a requested SDP authorization based upon a user multimedia Service Subscription;
309: The S-CSCF forwards the SIP Invite request with the SDP offer to a terminating UE;
310: An Offer Response returned from the terminating UE may be returned to the S-CSCF along the original signaling path;
311: The S-CSCF forwards the received Offer Response message to the P-CSCF;
312˜315: The P-CSCF triggers the SPDF to request the A-RACF to perform an admission control process based upon the parameters of the received offer and the offer response;
316˜319: The SPDF further performs a process of configuring an IMS connection for the C-BGF upon the success of the resource admission, and may optionally request the C-BGF to perform a NA(P)T binding process;
320: The P-CSCF feeds back the received Offer Response message to the originating UE.
As can be seen from the above described fixed origination flow, during the process of establishing an IMS session connection by the originating UE, the procedure of the resource admission control, performed by the A-RACF based upon the parameters of the offer and offer response carried in the admission request message sent from the SPDF, is performed prior to the IMS connection configuration processing executed by the SPDF for the C-BGF, such a procedure may result in the following problems:
If the SPDF requests the C-BGF to perform a NA(P)T binding process while performing the process of configuring the IMS connection for the C-BGF, the media stream address information after this NA(P)T binding process can be valid only for the A-RACF. Thus it would be meaningless to perform a resource admission control ahead of time before the A-RACF obtains the valid media stream address information.
In the above described NGN architecture established by the TISPAN, a Fixed Termination flow for establishing an IMS session is as shown in FIG. 4. Here, the Fixed Termination flow for establishing an IMS session mainly applies to a user within a home network, and the UE of the user is located in the home network, but has a registration on the IMS core network through xDSL. The detailed implementation process is as follows:
401: The SIP invite request, which contains the SDP offer and is sent from the originating UE, is forwarded to the S-CSCF of the terminating UE;
402: The S-CSCF determines a Service Profile upon receipt of the SIP Invite request with the SDP offer, and also invokes any initiation service logic required by the terminating party, including the procedure of performing a requested SDP authorization based upon a user multimedia Service Subscription;
403: The S-CSCF forwards the received SIP Invite request with the SDP offer to the P-CSCF in the terminating home network;
404˜407: The P-CSCF triggers the SPDF in the terminating home network to request that the A-RACF performs an admission control based upon the parameters of the received offer and the offer response.
408˜411: The SPDF reserves an IMS connection for the C-BGF upon the success of the resource admission, and may optionally request the C-BGF to perform a NA(P)T binding process;
412: The S-CSCF forwards the SIP Invite request with the SDP offer to the terminating UE according to the address information of the termination UE recorded during the registration flow;
413: The terminating UE sends an offer response message to the originating UE according to a subset of media streams, which is supported by the SDP offer and is sent from the originating UE, wherein the SDP offer may be indicative of one or more media of a multimedia session, and this offer response message would be sent to the P-CSCF;
414˜418: The P-CSCF triggers the SPDF to perform a process of configuring an IMS connection for the C-BGF, and may optionally further request the C-BGF to perform a NA(P)T binding process;
419: The P-CSCF forwards the offer response message to the S-CSCF;
420: The S-CSCF forwards the offer response message to the originating UE.
As can be seen from the above fixed termination flow, during the process of establishing an IMS session connection by the terminating party, the SPDF has already sent an admission request message to the A-RACF before the terminating UE receives the SIP Invite request, so that the A-RACF correspondingly performs a resource admission control according to the parameters of the offer and the offer response carried in the admission request message sent from the SPDF.
As a result, the A-RACF in the terminating home network can not obtain the valid media stream address information before the terminating UE receives the SIP Invite request, and it may become meaningless to perform a resource admission control ahead of time before the A-RACF obtains the valid media stream address information.